Dental plaque is being studied to determine if changes in microorganisms, specifically strep. mutans, occur during fluoride preventive procedures. The school population consists of children using fluoride rinses either daily or weekly, as well as some children using a placebo solution. Dental plaque samples are obtained periodically and analyzed using cultural methods and fluorescent antibody reagents specific for bacteria under study. Alterations in plaque composition during the study period will be related to the changes in the caries incidence.